Currently, commercially available secondary batteries include nickel cadmium, nickel hydrogen, nickel zinc and lithium secondary batteries. Among them, lithium secondary batteries have drawn much attention because of little memory effect to allow unrestrained charging/discharging, as well as very low self-discharging rate and high energy density, compared to nickel-based secondary batteries.
For such secondary batteries, lithium-based oxides and carbon materials are mainly used respectively as positive electrode active materials and negative electrode active materials. A lithium secondary battery includes an electrode assembly, which consists of a positive plate and a negative plate, with a separator therebetween, to which such positive electrode and negative electrode active materials are applied respectively, and an exterior material, i.e. a battery case, which stores and seals the electrode assembly along with an electrolyte.
Generally, lithium secondary batteries can be classified into a can-type secondary battery which integrates an electrode assembly into a metal can, and a pouch-type secondary battery which integrates an electrode assembly into a pouch made of an aluminum laminate sheet.
Recently, secondary batteries are widely used in middle- or large-sized devices like vehicles and power storage devices as well as small-sized devices like portable electronic appliance. When used in such middle- or large-sized devices, a plurality of secondary batteries are electrically connected in large numbers to increase the capacity and output. Especially, in such middle- or large-sized devices, pouch-type secondary batteries are usually employed because they can easily be stacked.
However, pouch-type secondary batteries are typically packaged in a battery case made of an aluminum/polymer resin laminate sheet, thus exhibiting insufficient mechanical rigidity. Therefore, when manufacturing a battery module with a plurality of pouch-type secondary batteries, frames are often employed to protect such secondary batteries from external shock, inhibit the movement thereof, and allow easy lamination.
Frames can be substituted for by other various terms such as cartridge, and are usually arranged in the shape of a rectangular plate with the center being empty, with the four sides encompassing the outer peripheral portions of pouch-type secondary batteries. In order to manufacture a battery module, a plurality of such frames are stacked and secondary batteries can be placed in inner empty spaces formed thereby.
On the other hand, when assembling a plurality of secondary batteries using such a plurality of frames, a plate-shaped cooling pin can be interposed between secondary batteries. Secondary batteries may be used in high-temperature environment such as in summer, and may generate heat on their own. In this case, when a plurality of secondary batteries are stacked on each other, the temperature of secondary batteries can be increased higher; and if the temperature becomes higher than suitable levels, the performance of secondary batteries may be deteriorated, even with the risk of explosion or fire in worse cases. Therefore, when manufacturing a battery module, a cooling pin is usually interposed between secondary batteries to prevent a rise in the temperature of secondary batteries.
Such a cooling pin is plate-shaped to be called a cooling plate, which is placed between secondary batteries in a battery module to cool secondary batteries in various forms and manners. Among such forms and manners to cool secondary batteries, air-cooling is typically and widely used to lower the temperature of secondary batteries via heat exchange between a cooling plate and air by allowing external air to flow around the cooling plate. For a battery module which cools secondary batteries using such air cooling, arranged is a cooling channel around cooling plates, which is connected to a duct to allow air to go into and out of the battery module.
However, for a battery module with such arrangements, gas generated from secondary batteries may be discharged to the outside via a cooling channel and a duct, causing some problems. In other words, gas likely to contain harmful substances may be generated while using pouch-type secondary batteries. If such harmful gas generated from secondary batteries infiltrates into a cooling channel, it may be discharged to the outside via a duct and then be inhaled into a user for such secondary batteries. Especially, hybrid cars and electric cars are equipped with middle- or large-sized battery pack including secondary batteries in large numbers, and they are thus more likely to discharge harmful gases generated from such secondary batteries. Also, if such harmful gas is discharged from a battery pack and flown into a duct, a driver inhaling the discharged gas may not only be exposed to direct bodily danger but also be more liable to traffic accidents because his or her driving ability is compromised during driving.